The present invention relates to electrophoretic deposition and, more particularly, to a method for the electrophoretic deposition of monolithic and laminated green bodies.
Precisely shaped, small ceramic bodies are used in many applications, including as pitch bonding capillaries in microelectronics, as high temperature nozzles, as ferrules for connecting optical fibers, as high temperature engine components, as dental crowns and as bearing parts. To achieve the precise shaping required for the first application, bonding capillaries, it has been necessary to use the process of cold pressing to fabricate ceramic capillaries.
Multilayer ceramic laminates, made of sequential layers of ceramics such as alumina and zirconia, are known in a variety of geometric shapes, including plates and discs. Applications of ceramic laminates include mechanical seals, automotive engine parts, furnace elements, multilayer and FGM substrates for hybrid circuits, capacitors, RF filters, and microwave components. The processes used to fabricate ceramic laminates include chemical vapor deposition (CVD) and physical vapor deposition (PVD), for layers less than about 1 micron in thickness; tape casting, for layers thicker than about 100 microns; and electrophoretic deposition (EPD), for layers between about 1 micron and about 100 microns in thickness, as will now be described.
Electrophoresis is a process in which charged ceramic particles suspended in a liquid medium are attracted to an electrode when an electrical field is imposed on the particles. EPD is the process of depositing a body of a desired shape on an electrode, using electrophoresis. EPD has long been used to form green ceramic bodies. In particular, EPD has been used by Sarkar, Haung and Nicholson (Electrophoretic deposition and its use to synthesize Al.sub.2 O.sub.3 /YSZ micro-laminate ceramic composites, Ceram. Eng. Sci. Proc. vol. 14 pp. 707-716 (1993)) to deposit laminated composites of alumina and yttria-stabilized zirconia (YSZ).
There is thus widely recognized need for, and it would be highly advantageous to have, a method of EPD that can be used in the fabrication of small, precisely shaped ceramic bodies such as connecting ferrules, orifices and micro-tubes.